I think there's a bug related to cave-ins...
I've previously mined out a large chunk of rock, and I used controlled cave-ins to do it (went faster that way), and everything went fine at first. It wasn't until I breached the caverns things started getting... weird.
This is what happens everytime I load the game:
Made no sense at first, I haven't dug in the place this happens (or anywhere near it) for like three years. It's no big deal, since all that happens is that some of my dwarves are knocked unconscious (it indirectly hits my statue garden), but it's quite annoying.
Well, now I noticed why this was happening:
There's mud. In an open space (several tiles of it actually, you just don't see it). The game doesn't seem to mind, except when you load it, because then it collapses (the mud remains though). It only started happening after I breached the caverns though, which also made plants start growing in those tiles. So now I got floating plants as well. Great. At least they disappear in the cave-ins.
On an unrelated note: Does anyone know a good way to reduce the amount of cats/kittens? As you can see in the second picture, close to the upper left corner, there's about a zillion cats (there are more than one/square). I'm butchering them as fast as I can, but the problem is that the sneaky bastards are getting tricky on me. They've figured out that if they "adopt" a dwarf, I can no longer kill them, so now they do that pretty much as soon as they're born. It's quite frustrating.